stirling run from motor hot coolant?

Discussion in 'Hybrid' started by oceandreams, Nov 14, 2010.

  1. oceandreams
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    oceandreams Junior Member

    I'm sure I'm going to get skewered here, but here goes.

    Typically how hot is the coolant coming out of a diesel motor or generator?

    In theory is it possible to install a Stirling motor in the cooling loop between the motor and it's heat exchanger, and turn a small alternator?

    Not looking to power an entire boat, just recapture a little energy just going to waste.
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You can run a thermal generator that will produce electricity without moving parts.
  3. mark775

    mark775 Guest

    In theory, yes. I think you are in good company with BMW and others, wanting to capture some of that energy. No reason to get skewered.
  4. oceandreams
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    oceandreams Junior Member

    These were next on the list. Any links to successful marine applications??
  5. michael pierzga
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    michael pierzga Senior Member

    Try Googling Solar Power, solar concentrator, Stirling Engine.

    I see people experimenting with solar Stirling engines on the net. They might be able to help you with the energy in heat, power out question.

    Attached Files:

  6. Boston

    Boston Previous Member

    there is a fan that you can buy for your wood stove that runs off the heat difference and I'm sure you could apply its technology to your system

  7. apex1

    apex1 Guest

    But you could lookup "Green steam power" to get a handle on that!
  8. Stumble
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    Stumble Senior Member

    As of now I don't know of any system designed to function with diesel engine exhaust, though some of the systems in testing phases might be applicable. My advice is to get in touch with some of the thermal differential engine makers and ask about the possibility of modifying their engines to work on a vessel, and suggest your boat as a working test platform if they are interested. I have done similar things in the past for a number of systems. Some manufacturers are excited by the possibility, some look for a closer option, but over the years I have gotten a couple of test systems installed with verying luck in getting them working. The up side is fun new always broken gear, but stuff that is fun to play with, and once everything worked as planned and I got to keep a couple of thousand dollars of equipment and they got a test platform.

    Just a little research gave me a couple of possible manufacturers of these systems:
    Are currently looking for Beta testers for their waste heat engines, specifically they are looking for someone with reciprocating or turbine engines to apply their systems too (One of many Beta testers they are looking for)
    Looks to be making much larger systems than those found aboard boats, but again you are trying to get into the R&D phase so this isn't necessarily a huge issue

    Orest Symko, a University of Utah Professor
    Is heading up a research lab doing work on converting heat to sounds to power. Again it may be a rough option, but if they are interesting there could be interesting results.
    Is focusing on heat sync type engines that remove residual heat from a system then convert in into power by cooling it through a hydrogen gas preasurization system. This sounds like a great idea to me where the cooling can be acomplished by a system similar to a keel cooler.

    Generally the engine exhaust of large diesel engines is below 100c which seems to be a necessary point for many of these waste engine systems to work. However coolant systems typically operate at around 95C so it may be possible to redisign the system so that the entering coolant is at 100+ and returns to the engine at reasonable temps. Not being a diesel mechanic I wouldn't want to speculate on the possibility.

    Stearling engines honestly seem to be the least likely option for this type of operation. They are traditionally finackie, hard to keep operating in harsh environments, and any type of bouncing seems to retard their production. But I wouldn't put it past an engineer to figure out something.
  9. apex1

    apex1 Guest

    The "green steam" engine is a valid excemption.

    Though we know, it is not what the OP wanted.

  10. Yellowjacket
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    Yellowjacket Senior Member

    About 30% of the energy coming from a internal combstion engine comes out the shaft, 30% is heat in the cooling system and about 30% comes out the exhaust. The temperature of the cooling system is about 100 C and the exhaust gas temperature is typically around 400C, so it is a lot easier to get energy from the exhaust than it is from the cooling system. If you look at the potential efficiency for a low temperature engine the amount of energy that you could get from the cooling system is about 10-15% of the energy in the cooling system, or about 3-5% of the output shaft power (30% that is in the cooling system multiplied by the efficiency of the bottoming cycle engine. So if you have a 100 hp engine, you are going to be able to get something on the order of 5 hp from the cooling system.

    Bottom line is that's hardly worth the trouble.

    If you used a bottoming cycle on the exhaust you may be able to get 20% of the available energy, which is likely on the order of 6 to 8 hp from a 100hp engine, which is some, but not a lot.

    As you can see, unless you have a lot of power coming from the engines there isn't a lot you have in terms of power gain.

    It's generally easier to make the power demand lower than it is to try to get energy from the exhaust or engine cooling system.
  11. apex1

    apex1 Guest


    but it sounds nice...
  12. Pierre R
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    Pierre R Senior Member

    If your diesel engine were sitting in a building driving something like a generator I would say go for it, its technically possible but if your diesel engine is in the bowls of a boat I would compare what you want to do with trying to take someones tonsils out by way of their *******. Its technically possible but not very feasible. You have a diesel engine sitting in a small engine room in a corrosive marine environment. The idea in boats is to keep things a simple as possible as every gadget takes three times as long to service or fix. Of all the places I would want to try it a boat would be the last place.
  13. oceandreams
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    oceandreams Junior Member


    Thanks for the info, not what I had in mind when I started the thread, but something to look at.

    Just so you know my thought process. You can buy a small educational unit that turns on the heat from a computer monitor. Something I can rest my hand on. 100C water will cause full thickness burns in seconds, so it at least seemed logical there might be enough energy to turn a small winding or (at the higher end) a small wind generator motor. Enough to possibly run house lights converted to 3-7w bulbs. Logical enough to ask the question anyway.

    What temp diff would you estimate to be needed? 500f? just curious not going any further with it (for now :) )

    Regarding the green steam: Regarding one design it was stated "this device produces up to 24 gallons of distilled water a day, charges batteries, and makes all the hot water you can use employing an ordinary household pressure cooker on a low simmering fire. This model steam engine operates the system on 4 to 20 psi of steam pressure." --You have my attention.

    In this thread in the first post It's stated that the psi to the machine is 100psi, but "the steam pressure is 3500-to 4000 is typical running a generator of about 5KW at around 100psi." Doing rough math at 20psi operational pressure that 700-800psi. When I was in the navy it was preached to us that the 1200psi superheated steam we used if leaking from a pinhole not only could be invisible but "decapitate you and cauterize the wound closed with almost no blood loss". Other ships used a 800psi plant and if memory serves me the warning applied there as well. Not sure I want my family anywhere near that. On a commercial boat with professional crew, sure, proven for over a century.

    You obviously have more experience and are a big proponent of steam, how is this implemented safely on the small-med boats we've discussed prior? A cooker on a pellet stove might work in Boston but not Tortola. All the examples a quick search found were for classic 1800's style boats.

    What about the cyclone ( ), what happens if there is a failure down the line?

    BTW did I see something about you owing a maritime museum?? Do you have a website I would be interested?


    It might not be economical practical presently but 1.8hp runs a 1000W generator, now to just figure out how..


    Good point, it was just something I'd thought about relating to a car several years ago when I first learned about the Stirling thought it might apply here
  14. Stumble
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    Stumble Senior Member

    A little more research led me to a company selling low energy systems (requiring tempratures of <500f) with experience already in applying these systems to diesel engines. Check out They at least claim to be able to generate around 50kw/hour from the combined heat of the exhaust and cooling system.

    For instance they claim to be able to generate 13KW/hr from the Exhaust, and 10KW/hr from the coolant system from a Caterpillar D175-2 (Which is actually a 175KW/hr generator with a 275 Horse Power engine). In adition they claim it might be possible to reduce the demands on the engine coolant system enough to save about 10hp dedicated to the radiator fan.

    If these claims are borne out, I could easily see replacing onboard generators with either these systems, or with fitting them onto smaller generator engines to produce the same net power. I plan on calling the company early this week to figure out exacally what the deal is with the systems, and if an installable product is on the market today. With a price of about 1KW hour/$1000 this could be a price competative system but I don't have enough info to really make a decision about it now.

  15. CDK
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    CDK retired engineer

    The easiest way by far to recover thermal energy is using a peltier thermoelectric device. Less expensive than a sterling motor and completely maintenance free.
    Because of the high initial cost you'll generate rather expensive electricity but at least have the satisfaction that it's green.

    Attached Files:

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